1. Field of the Invention
The present invention relates to large, stationary turbine power plants and more particularly to an axially loaded floating brush seal useful in large, stationary turbine power generators of the type used for utility services.
2. Description of the Prior Art
A typical stationary turbine power plant, known as Model Series 7001 simple cycle, single shaft, heavy-duty gas turbine (Frame-7 machine), is available from General Electric of Schenectady, N.Y. In this and similar gas turbines, a seal is located between an axial compressor rotor and a stationary inner barrel member, a chamber within the inner barrel member being supplied with cooling air from the last stage of the compressor by a controlled amount of leakage through the seal. A set of shaft bearings is located in the chamber.
Leakage in excess of a predetermined amount required for cooling of the bearings becomes parasitic and contributes to inefficiency of the turbine power plant. This is a serious problem in turbine power plants of the prior art, in that the labyrinth seals, which are positioned to limit the air leakage, degrade in operation because of thermal expansion and other factors that cause knife-edge labyrinth seal members and adjacent rotating elements of the seals to be worn away quickly, particularly during start-up and shut-down sequences. This is caused, for example, by thermal expansion and shrinkage of the inner barrel member being more rapid than the thermal expansion and shrinkage of the rotor at the seal. Thus, in the frame-7 machines, the bypass airflow may increase to approximately 100,000 lb/hr or higher from the 30,000 lb/hr that is considered optimal. Consequently, there is a loss of power that is believed to be between 1.5 MW (megawatts) and 3.0 MW.
Brush seals for aircraft gas-turbine engines are known, being disclosed, for example in xe2x80x9cBrush Sealsxe2x80x9d, Directions, September 1993. As disclosed therein, a brush seal consists of densely packed metallic bristles that are welded between a down-stream backing plate and an up-stream side plate. In a typical round seal for aircraft turbine applications, the plates are ring-shaped, the bristles extending radially inwardly at a trailing lay angle and making an interference contact with a rotor element, so that the bristles become curved and follow the rotor as it grows and shrinks during engine operation.
Brush seals have not been applied to existing large power plant turbines for a number of reasons. For example, the existing rotor components, being made from elements of low carbon steel alloys that are selected for certain thermal expansion properties, are believed to be unsuitable as wear surfaces for contact by the bristles, particularly during the extended operation cycles that are demanded of stationary power plants. Suitable hardening of applicable compressor rotor members is believed to be prohibitively expensive, particularly in existing equipment.
In U.S. Pat. No. 5,630,590, issued May 20, 1997 to Joseph P. Bouchard and Merrell W. Long entitled xe2x80x9cMethod and Apparatus for Improving the Air Sealing Effectiveness in a Turbine Enginexe2x80x9d, a brush seal is disclosed for use in a gas turbine engine. This patent is hereby incorporated in its entirety by reference.
In U.S. Pat. No. 5,961,279, issued Oct. 5, 1999 to Steve Ingistov entitled xe2x80x9cTurbine Power Plant Having Minimal-Contact Brush Seal Augmented Labyrinth Sealxe2x80x9d, a brush seal is disclosed for use in a gas turbine engine. This patent is hereby incorporated in its entirety by reference.
Both of these patents disclose fixed brush seals which are positioned on an end of the inner barrel with suitable spacing from the compressor rotor so that they do not engage existing rotor components. If engagement of the brush seal and the rotor components occurs, the engagement is a result of wobbling of the power shaft connecting the turbine and the compressor, differential expansion of the compressor components and the inner barrel of the machine and the like. As a result, the contact can result in a very high-pressure contact of the brush bristles with the existing rotor components since the bristles are fixed relative to the inner barrel. Accordingly, when contact occurs it can be very forcible, with resulting damage to the rotor components. As a result, clearance space must be provided to attempt to accommodate the worst-case situation. Accordingly, considerable air bypasses the bristles and as a result the use of a labyrinth seal in connection with the bristles is disclosed.
The use of a labyrinth seal in itself entails substantial difficulties with respect to start-up and shutdown operations. These shortcomings are discussed at considerable length in both of the patents discussed above.
Since it is desirable, for the reasons discussed above, to control the amount of air passing between the rotor components and the chamber inside the inner barrel, improved sealing methods have been sought.
The invention comprises a stationary gas turbine engine for a power plant having an axially loaded floating brush seal and comprising:
a) a multistage axial compressor, the compressor having a rotor, the rotor having a radial surface downstream of at least a major portion of the compressor:
b) a turbine shaft-coupled to the rotor;
c) a stationary inner barrel member having an end and a cavity positioned in the end of the inner barrel member, the cavity having an inner surface, the inner barrel being downstream of at least a major portion of the compressor, air flowing from the compressor passing outside of the inner barrel member, a chamber within the inner barrel member forming a passage for cooling air from the compressor, the cooling air flowing from the chamber and being mixed with combustion gases upstream of the turbine;
d) an axially loaded floating brush seal for controlling air passage into the chamber from the compressor, the axially loaded floating brush seal comprising:
(i) a bristle holder axially positioned relative to the inner barrel;
(ii) a multiplicity of bristle members extending axially from the bristle holder toward the radial surface of the rotor, downstream bristle member ends being rigidly retained relative to the bristle holder;
(iii) a back plate connected to a downstream end of the bristle holder and having its downstream side adapted to engage a spring; and,
(iv) at least one spring mounted between the back plate and an inner surface of the cavity to urge the bristle members into contact with the radial surface of the rotor.
The present invention further comprises a stationary gas turbine comprising:
(a) a first rotary compressor component having a rotor having a radial surface;
(b) a non-rotary second component having an end extending over and around at least a portion of the rotor with an end near the radial surface and including a cavity;
(c) a passageway between the end of the second component and the rotor; and,
(d) an axially loaded floating brush seal positioned on the end of the second component to resiliently engage the radial surface, the floating brush seal comprising:
(i) a bristle holder axially positioned relative to the second component;
(ii) a multiplicity of bristle members extending axially at their first ends from the bristle holder toward the radial surface of the rotor, second ends of the bristle members being rigidly retained relative to the bristle holder;
(iii) a back plate connected to a downstream end of the bristle holder; and,
(iv) at least one spring mounted between the back plate and an inner surface of the cavity to urge the bristle members into contact with the radial surface of the rotor.
The present invention further comprises a method for controlling cooling air flow into a chamber in a stationary inner barrel member in a turbine power plant having a multi-stage axial compressor, a turbine shaft-coupled to a rotor of the compressor, the rotor having a radial surface positioned circumferentially relative to the shaft and near an end of the stationary inner barrel member, the method consisting essentially of:
(a) positioning a brush seal comprising:
(i) a bristle holder axially positioned relative to the inner barrel;
(ii) a multiplicity of bristle members extending axially at their first ends from the holder toward the radial surface of the rotor, second ends of the bristle members being rigidly retained relative to the bristle holder;
(iii) a back plate connected to an end of the bristle holder; and,
(iv) at least one spring mounted between the back plate and an inner surface of a cavity in the end of the inner barrel to urge the bristle members into contact with the radial surface of the rotor; and,
(b) providing substantially all of the cooling airflow required in the chamber via at least one flow-controlled passageway in fluid communication with at least one of a compressor outlet and an auxiliary air source and the chamber.